synergies?

[KrimsonTwilight]

What are they? How do I get them and how do they help me?

[saellison]

Synergies are skills that add a bonus to another skill. If you toggle over a skill on the skill tree it will list details about the skill and list what the other skills will add to it. For instance, the paladin skill Blessed Hammer when toggled over lists a description of the skill, its damage, and it says that the skills vigor and blessed aim add 14% damage with every skill point invested in them. So if you wanted to make a blessed hammer paladin using blessed hammer as your main skill you would max out blessed hammer and the two synergies for the damage bonus they provide. It is impotant to note that a only points you put in the synergy refered to as "hard points" count towards the synergy bonus. +skills from equipment do not provide the synergy bonus.

[Thyiad]

Synergy relationships (http://www.chrisclarke.co.uk/D2stuff/PDFs/Synergy_relationships/) in pictures.

Basically they increase the effectiveness of attacks.

Skills calculator (http://diablo2.ingame.de/spiel/skills/calc/index.php?lang=en)
Hammerdin calculator (http://www.darkmasters.de/calc/hammadin_110_eng.php)
Have a play with those, that should help you understand it.